Battle of Mons Eretum

The Battle of Mons Eretum occurred in 329 BC when an army of Umbrian Gauls attempted to attack the city of Rome, the capital of the Roman Republic. The acting commander of the Roman Senate's legions Decius Rabirius Silo and the Roman paterfamilius Gaius Julius left Rome with a sizeable Roman army and encountered the warlord Dumnorix's Gaulish army along the Tiber River near Mons Eretum (present-day Monterotondo, Lazio, Italy). The Roman army was divided between the main army of Silo, which was positioned to the south, and Julius' army across the Tiber to the east. The Gauls therefore had to divide their attention between both armies, and the Romans launched a successful flank attack, resulting in the collapse of the Gaulish army. Rome was safe from barbarian threat for a while, and the Romans would go on to take much of the peninsula from the barbarians in the following years.

Background
The Italian Peninsula was once inhabited by a myriad different peoples, with the Samnites living in the south, the Romans in the center, the Etruscans in the northwestern region of central Italy, and the Gauls living in the north and the northeast; the Greeks set up some colonies along the coastline, known to the Romans as Magna Graecia. The Gaulish barbarians inhabited the region of Umbria, and they came to be known as the "Umbrian Gauls" due to their descent from the tribesmen of Gaul (present-day France). The unwashed Gaulish barbarians (specifically the Senones) sacked Rome in 387 BC, and conflict between the Romans and Gauls became the norm in northern Italy.

Dumnorix's invasion of Italy
In 329 BC, the Gaulish barbarian warlord Dumnorix led a war band of 452 warriors south from Umbria into central Italy, intending to pillage and plunder the Roman countryside. The Gauls massacred Roman villagers and burnt down villages, terrorizing the Roman people. As a result, Roman Senate leader Sisenna Petillius Cato ordered the Roman patricians Gaius Julius and Decius Brutus to move north and battle the invaders, as well as conquering the tyrants of Tarquinii. The Romans would have to focus on the imminent Gaulish threat first, however, as the Gauls penetrated into Latium and managed to make it to the countryside just outside of the capital. The Roman Senate's acting legion commander Decius Rabirius Silo was sent out of the city of Rome with 430 troops, while Julius led 106 of his own troops out of Rome to assist Captain Decius' army in fighting off the Gauls.

Battle
The Gauls arrived on the field of battle in the north, while the senate's army arrived to the south; the Julii deployed to the east of the Tiber River. Neither army stomached the will to fight, leading to some skirmishes between the Gauls and the senate's forces. However, Gaius Julius decided to use this opportunity to deploy his soldier closer to the bridge over the Tiber, and some Gaulish warriors crossed the Tiber to attack the Romans. The Roman cavalry charged the Gauls, massacring them, and the Gallic cavalry that moved across the river to attack the Roman archers was slaughtered by spear-equipped triarii. This allowed for Julius to lead his forces across the Tiber to surprise the main Gallic army, which began its all-out assault against the senate's army. Captain Decius' forces took heavy losses, as most of them were peasants, but the arrival of the Julii army assisted the senate's forces, as the Gauls were flanked. The Gauls collapsed under pressure from the front and flank, and their forces broke as their fighters were decimated. Dumnorix was forced to retreat, and the Gallic invasion was defeated.

Aftermath
The battle of Mons Eretum was a great victory for the Roman Republic over the hairy Gaulish barbarians, and the Gauls had no warriors left to attempt another invasion of Rome. The Roman victory allowed for the Julii to focus on capturing Tarquinii from the Etruscan tyrants, and the Gauls of northern Italy would be subjected to Roman rule and slavery after being thoroughly defeated several times.